# CVE-2026-55660: TinaCMS: Cross-origin postMessage handlers and rich-text URL-sanitization bypass enable stored XSS and session takeover

> Attackers can exploit unverified postMessage handlers and URL sanitization flaws to inject scripts and hijack authenticated editing sessions in TinaCMS.

- **Severity:** High 7.6 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Jul 2026
- **Updated:** 2 Jul 2026
- **Also known as:** GHSA-g5qx-h5f3-mp2f

## What is CVE-2026-55660?

CVE-2026-55660 is a high-severity cross-site scripting vulnerability in @tinacms/app, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Tina is a headless content management system. In versions prior to @tinacms/app 2.5.6 and tinacms 3.9.3, cross-origin postMessage handlers and a rich-text URL-sanitization bypass enable stored XSS and session takeover. The library registers window message listeners — the useTina overlay handler, the OAuth authentication popup handler, and the admin↔preview iframe GraphQL reducer — that act on event.data without verifying event.origin or event.source and post messages using non-specific target origins, while insufficient URL sanitization in rich-text content allows malicious URLs to persist and execute. A page the victim visits (or a window in an opener/iframe relationship with a Tina admin) can forge messages to drive the editor, inject preview content, or observe/forge the OAuth popup channel to take over an authenticated editing session. This issue has been fixed in versions @tinacms/app 2.5.6 and tinacms 3.9.3.

Weakness: CWE-940 (Improper Verification of Source of a Communication Channel), CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-601 (URL Redirection to Untrusted Site), CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-55660?

4 open source packages ship an affected version, including @tinacms/app and tinacms.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@tinacms/app` | npm | All versions | 2.5.6 |
| `@tinacms/app` | npm | All versions | 2.5.6 |
| `tinacms` | npm | All versions | 3.9.3 |
| `tinacms` | npm | All versions | 3.9.3 |

## How do I fix CVE-2026-55660?

Upgrade @tinacms/app to 2.5.6 or later.

## Is CVE-2026-55660 being exploited?

There is no known exploitation of CVE-2026-55660 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55660 and fix it if it is affected.

What it is: CVE-2026-55660 is a high-severity cross-site scripting vulnerability in @tinacms/app, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-55660 in the wild and no public exploit code.

Affected packages and fixed versions:
- @tinacms/app (npm): affected all versions; fixed in 2.5.6
- @tinacms/app (npm): affected all versions; fixed in 2.5.6
- tinacms (npm): affected all versions; fixed in 3.9.3
- tinacms (npm): affected all versions; fixed in 3.9.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55660/ (Markdown: https://insights.sbomify.com/CVE-2026-55660/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55660
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55660
- OSV: https://osv.dev/vulnerability/CVE-2026-55660

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55660/
Summaries are generated and may contain mistakes; the official description above is the record.